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anonymous

  • 5 years ago

I am having the most difficult time trying to understand a problem with the formula a=pe^rt, where A=amount accumulated, p=principal, r=interest rate, and t=time in yrs. What principal should be deposited at 7.405% to ensure the account will be worth $18,000 in 11 years

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  1. anonymous
    • 5 years ago
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    18,000 = p(1+.07405)^11

  2. anonymous
    • 5 years ago
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    So 18,000=(1p+7405p)^11, right?

  3. anonymous
    • 5 years ago
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    First step would be to add (1 + .07405) to get 1.07405 Then take that to the ^11

  4. anonymous
    • 5 years ago
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    2.194166065

  5. anonymous
    • 5 years ago
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    I thought the formula was A= p/e^rt

  6. anonymous
    • 5 years ago
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    Good now you have 18,000 = 2.194166065p so divide both sides by 2.194166065

  7. anonymous
    • 5 years ago
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    8203.572322= p

  8. anonymous
    • 5 years ago
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    or $8203.57?

  9. anonymous
    • 5 years ago
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    OK.. we can do it your way... just a minute.

  10. anonymous
    • 5 years ago
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    18,000 = P e^(.07405*11) 18,000 = Pe^.81455 18,000 = P 2.258 Divide by 2.258 $7971.66

  11. anonymous
    • 5 years ago
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    How do you calculate e?

  12. anonymous
    • 5 years ago
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    I plugged it into the calculator... I have an e^x key.

  13. anonymous
    • 5 years ago
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    Wait just a minute

  14. anonymous
    • 5 years ago
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    Also the ln key right?

  15. anonymous
    • 5 years ago
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    Ok, I got the same thing you got this time.

  16. anonymous
    • 5 years ago
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    I am not used to the e function.. here is an example, I will do yours for you following this example So 130000 = 1949 e^(.00835 t) Take logs of both sides: ln 130000 = ln 1949 e^(.00835 t) = ln 1949 + ln e^(.00835 t) = ln 1949 + .00835 t t = (ln 130000 - ln 1949) / .00835 = (ln 130000/1949) / .00835 which you have to calculate using a calculator

  17. anonymous
    • 5 years ago
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    18,000 = Pe^(.07405 * 11) 18,000 = Pe^.81455 ln 18000 = ln P + ln(e^.81455) ln 18000 = ln P + .81455 9.79813 - .81455 = ln P 8.98358 = ln P e^8.98358 = e^ (ln P) $7971.12 = P

  18. anonymous
    • 5 years ago
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    ok. It was the "e" part that was throwing me off. But what you and I got is what the book has also.

  19. anonymous
    • 5 years ago
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    Great... A little out of my league... but I am glad we got it.

  20. anonymous
    • 5 years ago
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    Now, with the formula with A =p(1+r/n)^nt A = $982500 p+71500, t=17yr

  21. anonymous
    • 5 years ago
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    Don't we have to know either r or n?

  22. anonymous
    • 5 years ago
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    I have 98, 2500=71, 500(1+r/n)^17. Do you know how I would find r/n?

  23. anonymous
    • 5 years ago
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    R is what they are asking for. R is a percent

  24. anonymous
    • 5 years ago
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    What is n?

  25. anonymous
    • 5 years ago
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    Here's the question: For compound interest accts, the amount A accumulated or due depends on the principal p, interest rate r, number of compounding per year n, and the time t in years according to the formula A=p(1 + r/n)^nt. Find the r given A=$98, 250, p=71,500, and t=17 yr with interest compound monthly

  26. anonymous
    • 5 years ago
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    compounded monthly means that n = 12

  27. anonymous
    • 5 years ago
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    982,500 = 71500(1 + r/12)^12*17

  28. anonymous
    • 5 years ago
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    oh, because 12 represent the "per year"

  29. anonymous
    • 5 years ago
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    982,500 = 71,500(1 + r/12)^204

  30. anonymous
    • 5 years ago
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    divide both sides by 71,500

  31. anonymous
    • 5 years ago
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    13.7412587 = (1 + r/12)^204

  32. anonymous
    • 5 years ago
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    13. 74128874=(1+r/12)^204

  33. anonymous
    • 5 years ago
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    Now you have to get rid of the ^204 you do that by taking the 204th root of both sides. Use the x sqrt(y) key on your calculator

  34. anonymous
    • 5 years ago
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    1.012927965 = 1 + r/12

  35. anonymous
    • 5 years ago
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    Subtract 1 from both sides

  36. anonymous
    • 5 years ago
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    .012927965 = r/12

  37. anonymous
    • 5 years ago
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    multiply both sides by 12

  38. anonymous
    • 5 years ago
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    12.155 = r

  39. anonymous
    • 5 years ago
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    ON the step with the sq rt of 13.7412587 I got an error msg

  40. anonymous
    • 5 years ago
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    Your saying 204 sq rt 13.7412587 correct?

  41. anonymous
    • 5 years ago
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    You are not taking the sqrt root.. Find the key that has x sqrt(y) type in 13.7412587 hit the xsqrt(y) key and then type in 204 and hit enter

  42. anonymous
    • 5 years ago
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    I dont believe I have that key

  43. anonymous
    • 5 years ago
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    Are you operating a TI-84?

  44. anonymous
    • 5 years ago
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    NO.. just a calculator on my computer the basic one..

  45. anonymous
    • 5 years ago
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    Let me see if I can find a TI-84 on line and tell you what it looks like

  46. anonymous
    • 5 years ago
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    How about under MATH option 5 does it show an x and then a radical sign

  47. anonymous
    • 5 years ago
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    yes

  48. anonymous
    • 5 years ago
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    You want the x to be the 204 and under the radical sign to be the 13.xxxxxx Try it and see if you can get what I got.

  49. anonymous
    • 5 years ago
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    YES!!!! I got it! such a relief! thank you very much

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